Bacteria have big influence on human's daily life. They affect human health and cause illness and death. So, it is very important to fight against bacteria. Until now, most of the antimicrobial agents fighting bacteria are small molecule chemicals. They are used in many applications such as anti-bacterial hygiene products, food preservative . . . etc. They can also be used as water or soil sterilization. Small molecule antibacterial agents have inherent problems such as residual toxicity to the environment, the short-term antimicrobial effect, easy to be absorbed by the human body . . . etc. One way to solve these problems is to use antimicrobial polymer instead of small molecule antimicrobial agent.
The use of antimicrobial polymers offers promise for enhancing the efficacy of some existing antimicrobial agents and minimizing the environmental problems accompanying conventional antimicrobial agents by reducing the residual toxicity of the agents, increasing their efficiency and selectivity, and prolonging the lifetime of the antimicrobial agents. (quoted from Biomacromolecules, 2007, vol. 8, No. 5, page 1359-1384)
Since many antimicrobial applications are in aqueous or hydrophilic environment, such as preservatives for cosmetic, antibacterial hand sanitizer, antibacterial cleansers . . . etc. So there is a need for developing water-soluble antibacterial polymer.
Since ancient times, the antimicrobial effect of silver is well known and applied by human in their daily life. In early times, people made food container from silver because they found out that food or milk in silver container were preserved longer than in other kind of containers.
Till modern time, silver for antimicrobial application has extended to different forms such as silver ion and nano silver.
The antimicrobial silver ion is mostly existed in the form of salt such as silver nitrate, silver acetate and silver thiosulfate. However, most of the other salts of silver have low solubility in water.
Other than the salts mentioned above, silver ion can also form complex with organic molecule. The most famous one is silver sulfadiazine. It is widely used in treating burning wound. However, silver sulfadiazine, like most of the silver salt, has low solubility in water.
All the antimicrobial silver salts and antimicrobial organic complex mentioned above are still small molecules. They have all the drawbacks of antimicrobial small molecules. In order to combined the good antimicrobial property of silver ion and the benefit of polymer, the development of water soluble antimicrobial polymeric silver salt is very necessary.
Silver ion can be complexed with polymer to form polymeric silver salt. The polymeric silver salt has the same problem of low solubility in water. British patent GB420533 (A) disclose the preparation method of silver polyacrylic acid. Although the raw material, sodium polyacrylic acid, is soluble in water, the silver polyacrylic acid product cannot be dissolved in water. The objective of GB420533 (A) is to use silver polyacrylic acid as a general plastic material instead of antimicrobial polymer.
U.S. Pat. No. 5,709,870 discloses a water soluble silver containing antimicrobial carboxymethylcellulose (CMC). The preparation is done by suspending sodium CMC in water and exchange sodium with silver using silver nitrate. However, the silver content in polymer is lower than 1%.
In an article published in 2001(Pharmaceutical chemistry Journal, 2001, vol. 35, No 5, Page 252-253), a silver containing water soluble antimicrobial polyacrylic acid with chemical structure of (CH2CHCOOH)n—(CH2CHCOOAg)m (n=9000˜40000 and m=100˜3000), the silver content between 4˜10%) is presented. It is mentioned in the paper that the silver containing polyacrylic acid can be dissolved in water and has good antimicrobial property. However, in that paper, no preparation method is shown. Yet, in Russian patent RU2220982 filed by the same author, the preparation process is disclosed. The process includes steps of first mixing silver nitrate aqueous solution and polyacrylic acid aqueous solution together, stirring for 30 to 60 minutes and then drying at 50° C. to give a grey transparent product. It is obvious that no pure silver containing polyacrylic acid was separated and obtained by the preparation process of the Russian patent.
It is well know that among all the water soluble polymer, polyacrylate is the most versatile water soluble polymer. However, until now there is no water soluble antimicrobial polyacrylate silver salt been designed and synthesized so far.